Carrying out experiments on thermal stabilization of chips, researchers of the S.S. Kutateladze Institute of Thermal Physics (RAS Siberian Branch) once noticed this phenomenon: a locally heated liquid flowing under the effect of gravitation gives rise to odd structures looking like relief features, or a set of hollows and rises. It attracted the notice of physics and mechanics researchers. In fact, they came to deal with a new type of instability. Such structures, it is thought, can be used for intensification of heat and mass transfer processes, namely in film evaporators widely used in the production of sugar, fruit and vegetable juices and sea water distillation.
A team of research scientists at the M.A. Lavrentyev Institute of Hydrodynamics (RAS Siberian Branch) under RAS Corresponding Member V. Pukhnachev took up this problem. Next came the Copernicus Program which also involved scientists from the Microgravitation Research Center at Universite Libre (Brussels, Belgium). Although space research scientists, they undertook a down-to-earth research project for the food industry.
The Copernicus Program was fulfilled with much success in 2002, and a joint report was filed on its results. Dr. Kabov, physicist and mathematician, who headed the Russian research team, made a communication at a conference on heat transfer held at Grenoble, France.
The theoretical and practical results thus obtained paved the ground for a joined program dubbed "Relief slated for realization at the international space station Alpha.
But why should such kind of "relief' structures be studied in outer space? As Dr. Kabov sees it, liquids and biphasic currents in particular are much acted upon by the gravitational impact here on the earth's surface. The gravitational force interferes with processes under study. But space experiments give an objective picture of the processes taking place in liquids and, with the aid of video cameras,
allow to measure essential parameters. Such data will be of much help to space hardware designers in developing life support systems. Besides, important information will be obtained for upgrading ground-based technologies and for gaining a broader view of processes occurring on earth. And last, this information will be essential for the development of science.
Today research physicists are grappling with a formidable problem of developing a model of a liquid's decomposition at uneven heating and at jet flow, and studying its behavior under the effect of gravitation and at zero gravity. A good many factors should be explored: how a liquid changes its physical characteristics, and how heat transfer proceeds under different conditions.
Simultaneously, research teams are checking up on experimental models at the Novosibirsk-based laboratory, and in Belgium as well, where Professor J. -C. Legro's group is working. For this purpose an experimental stand was taken to Brussels from Siberia. Events were registered by a high-rate digital video camera, and interesting observations were obtained with its help. Crushed aluminum was strewn over the surface of a liquid so as to follow its movement. At a definite point the liquid ran into an obstacle, with its particles deflected to the right or left. A small portion of the liquid spilled over the "stumbling block", while its larger part flowed by on both sides. Here different forces were at work-those of inertia, of gravitational pull, and many others. The existence of a point of stagnation-or rather, a stop line-was proved, whereupon the liquid starts moving upwards. This phenomenon was predicted by calculations made by Dr. Pukhnachev's group.
A good deal is now known about the physics of the new structures. Research scientists have learned to forecast at what particular moment such "relief features" show up in a liquid, their parameters, wavelength, and what occurs at the interface of heating. However, computer simulation models of these structures have to be synthesized, we cannot yet calculate their origination dynamics and control them. It is not quite clear yet why suchlike structures should come to be. We can learn only from experiments under microgravitational conditions.
After the Grenoble-held conference, Dr. Kabov worked for a time on board a flying laboratory. That was a stage preliminary to the joint "Relief experiments. The lab flew over the Atlantic Ocean along the western coast of France. A jumbo aircraft was re- equipped to simulate outer space conditions; moving up, it caused micro-gravitational conditions for a mere 20 - 22 seconds, so the research team on board had to be on the lookout and act quickly. Thereupon the liner changed its trajectory, now nose-diving, now zooming up.
The experimental research team also included biologists and kinetics experts. All measurements were made with the aid of sensors. A computer registered the data. A video camera recorded all events aboard the craft. As Dr. Kabov says, their team could watch many new regimes of biphasic flow movement. However, the results obtained during these flights must be processed and evaluated. This work is in full swing now. But the chief task of the flying lab experiment was accomplished: an equipment checkup at weightlessness.
Nauka v Sibiri (Science in Siberia), 2003
Prepared by Olga BAZANOVA
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